Would it go down virtually instantly like the old W? That would be OP since she'd have basically no counterplay for her twin fang damage.
Does it still have a delay and start at a smaller AoE? Then she'd probably be pretty useless since her current Q is dodgeable and the enemy would just not stand in the zone as it expands so they can out-trade her.
What duration is the applied poison for when they move out of the poison? A shorter duration makes it harder to get anything out of the twin fang bonus damage, especially against mobile targets that can leave the zone after they've been hit with it, a longer duration (as much as current Q) puts a really big high-end damage output for enemies that get hit with cc and have to stand in a landed Q, basically doubling the duration, which can risk making her very feast/famine depending on team synergy.
No matter how it ended up balanced, it would also create a lot of "don't walk here" zones in a fight when she already produces a pretty big "don't walk here" zone, that's a lot of visual noise from just one out of ten champions for both sides to process.